The present invention relates to an image forming apparatus designed so that a photosensitive member is subjected to fatigue treatment advance of the copying operation.
In a copying apparatus which has a high-sensitivity photosensitive member capable of establishing electric potential thereon by being subjected to electrification, it may be known in the art that the charge-establishing property of the photosensitive member somewhat changes with respect to operation time period and saturates within an allowable range of steady operating condition. After stopping the copying apparatus, the photosensitive member recover the changed charge-establishing property with respect to rest time period.
As one example of the charge-establishing property, a photosensitive member having a fatigue characteristic will be explained in which the charge establishing property deteriorates or lowers somewhat with respect to operation time period and the lowered charge establishing property due to running fatigue recovers with respect to rest time period. Accordingly, with a long time duration between a copying operation and the next copying operation, the photosensitive member recovers from fatigue, thus causing fogging and an increase in copying density. In order to prevent this problem, a photosensitive member is subjected to fatigue treatment in advance of the copying operation of the copying apparatus.
For example, in order to subject a photosensitive member to fatigue treatment, an apparatus disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 102862/1981 repeats dozens of times, the electrifying, exposing, and neutralizing operations toward a photosensitive member of ZnO during a warming-up of the fixing heater. Another apparatus disclosed in Japanese Patent Examined Publication No. 52428/1984 is so designed that a photosensitive member is prerotated an increased or decreased number of times in proportion to the rest time, i.e. the time which has passed without performing copy operation since turning on the power under the inhibition of the copying operation, so that the uniform imagewise exposure is performed in the area between an electrifying unit and a developing unit. Another apparatus, disclosed in Japanese Patent O.P.I. Publication No. 25752/1981, is so designed that a photosensitive member is irradiated with neutralizing light, exposure light, or the like during a warming-up of the fixing heater.
However, into any of the above mentioned apparatus, such considerations are not incorporated as to the temperature of photosensitive member, nor the dead time after turning the power off to turning the power on again. Further, into the apparatus disclosed in Japanese Patent O.P.I. Publications No. 102862/1981 and No. 25752/1981, such considerations are not incorporated as to the recovery of a photosensitive member from fatigue due to the rest time after the completion of warming-up i.e. the rest time after the first subjection of fatigue treatment until the start of the actual copying operation, nor the recovery of a similar member from fatigue due to the passage of time during a long idling period i.e. the rest time period which has passed while maintaining power on without the copying operation. Therefore, none of the above mentioned apparatus are adequate, especially regarding the proper control of the image density for a certain number of copying sheets at the start of the image forming operation, to obtain a satisfactory image without causing fogging and an increase in copying density.